Current electronic devices utilize touch-sensitive screens to receive an input from a user. Most of these screens have the ability to detect either the x-y position of the finger touched the screen or the amount of the force applied. Projected or surface capacitive touch screens are widely used in such electronic devices to sense the x-y position of the fingers. However, they are only responsive to capacitive objects such as human fingers or a stylus or any other object that is capacitive. But such screens do not have the capability to detect the amount of the force applied, limiting the user experience. Other capacitive touch screens are meant to provide 3-dimensional information such as the inventions disclosed in US20120013571 A1 and US8169416B2. However, these inventions are based on parallel plate capacitor configurations in which the stroke of the plate is limited to one third of the initial gap between the capacitor plates. To make such a configuration highly sensitive, the gap between the plate electrodes has to be small; which in turn limits the dynamic range of the sensor in terms of the range of the force applied.
Piezoresistive touch screens offer the ability to detect the x-y position and the amount of the force applied. However, such technologies suffer from low sensitivity when the forces applied are limited to a small range, such as when a finger touch is applied. In addition, these piezoresistive touch sensors are sensitive to temperature changes. These type of touch screens are also complex in structure as they might contain liquid cells. An example of such screens is presented in US Provisional Patent Applications No. US20130096849 A1, 2014/0007705 A1, and US 20150138112 A1.
The present invention of a touch-sensitive interface module, which is based on a MEMS piston-tube capacitive force sensor, is able to overcome the limitations of conventional capacitive touch screens.